When it comes to hydraulic valves, especially hydraulic valves used in driven machines, safety precautions have to be taken so that the hydraulic valves do not trigger movements that pose a hazard to their environment. For this reason, particularly in the case of hydraulic valves that have solenoids to move a control spool, care is taken to ensure that the solenoids cannot be inadvertently energized.
The solenoids are driven by output stages that are powered by a voltage supply. In addition to the switch-off function of the output stages, which switch their outputs high-ohmically during the switching-off, as a safety measure, it should be possible to disconnect the output stage from the supply voltage by means of a switch.
Data sheet RD 95200 of the Bosch Rexroth company dated June 2007 shows a control device for a hydraulic valve having a central safety shutdown. Here, however, the problem arises that the components employed for the safety shutdown are likewise subjected to ageing processes, and a failure of the central safety shutdown can give rise to undesired reactions in the system that is actuated by the hydraulic valve.